There's NO reason to support Mcallister as Red John. This is why we will never have an explanation or revisit Red John, even if we were to confront Heller for answers, because the writers themselves can't come up with enough evidence to support it. It's not 'clever' or 'good writing' to make the one person who could not possibly have been Red John suddenly be Red John this whole time; Thomas Mcallister has had the least fans theorize him as Red John for good reasons.

1. It actually takes longer to get to Tijuana, Mexico from Napa County than it does to get to Tijuana, Mexico from Sacramento. If Red John is supposedly the Sheriff, who would have to be working at this time in Napa County, Jane and co. should have arrived at least minutes before Red John could get to Jared Renfrew and kill him, since they left right away. The only explanation for this is that the oh so convenient Blake Association had corrupt officers at the Mexicali border to kill Jared Renfrew and plant 'He Is Mar' on the wall above him. Is that so hard to explain, writers of The Mentalist?

2. Despite the above, the man who calls Jane whilst in Jared Renfrew's hotel room laughs into the phone, and it sounds undeniably British a la Brett Stiles.

https://www.youtube.com/watch?v=ED9ngcO4cz4

It's obvious this is Red John, and it's not the Sheriff. At this point in the series, Bret Stiles and Ray Haffner are far more likely candidates than Mcallister ever was.

3. "Red John and Jane are very much alike"; "relentless manipulation" according to Lorelei Martins
and Jane about what Lorelei said, and we see this; they both have powers
of mentalism. They both enjoy tea. They both don crisp, clean suits as casual wear. When they say "someone like Jane" and "relentless manipulation", what comes to mind?
The first thing that comes to my mind is Visualize and its countless manipulated
followers, the doing of Bret Stiles. In what possible way is Thomas Mcallister like Patrick Jane? None. Period.

4. Later, when recalling the names of everyone he has shook hands with since his incident, Patrick Jane rules out people who he never saw or heard from again...This, in turn, immediately rules out Thomas Mcallister, who Jane never saw or heard from again after Red Hair and Silver Tape.

5. How does Red John glean Jane's final list of suspects before he could narrow it down himself, and learn of his happy memory in his past? Because he is a real psychic? HAHAHA. NO. One glaringly obvious explanation for this is that Red John, using his own skills of hypnosis he used on Rosalind Harker and Kristina Frye to make her catatonic, plants these name suggestions along with his own so that they can meet eventually, and fishes Jane's memories for something of use to freak him out, if for no other reason than to stroke his own ego. Sweet and simple. This is also how Red John could have been able to plan all of his next moves out perfectly by using these people on the list as pawns over the course of two months prior to Jane seeing the video. I can buy that, after all we have seen Jane capable of. HOWEVER, Mcallister does not fit this role at ALL. Once again, Brett Stiles or a Visualize apprentice, Ray Haffner, are plausible.

In regard to all the analyses of Red John throughout the series: Red John is like Jane, well spoken, listens to classical music, reads classical texts, drinks tea, wears suits, has short, straight hair. He has powers of mentalism, hypnotizing Rosalind Harker as well as Kristina Frye into a catatonic state, possibly implanting the final list of suspects into Jane's mind, and if not this, at the very least we know he extracted a memory from Jane's psyche. The Sheriff, even amongst people not associated with Jane, does not once demonstrate he fits this description. In fact, in the only episode he appears (Red Hair and Silver Tape) before he is nonsensically plugged into season six as unnecessarily creepy going completely against how he is portrayed in the episode he debuts, he is literally a balding small time hick. Incompetent in speech. Incompetent in manner. Incompetent in duty. Poor imitation of Red John's voice. No suits. No tea. No hair. No tricks. No mask. No linoleum knife. Jane did not see or hear from him again after Red Hair and Silver Tape.

Bullshit.

Fuck you, Heller, for not honoring your own art. Fuck Warner Brothers and fuck Peter Roth for forcing Heller to kiss his ass and prematurely ruin the show. May their shitty careers come to a swift and well-deserved end.